JP2001127378A - Semiconductor integrated element and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor integrated element in which no climbing growth up to a mask occurs during selective growth even if the film thickness of a layer is increased when different layer structures are butted for joint, especially such a narrow irradiation semiconductor laser element that can operate at a low threshold current. SOLUTION: In this semiconductor laser element, an active layer area I of layer structure including an active layer and a waveguide layer area II butt- joined therewith are formed on a semiconductor substrate, and the butted joint surface J is a vertical surface inclined at 45 degrees to the crystal azimuth (011) of a conductor material comprising at least the active layer in the active layer area I.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor integrated device and a method of manufacturing the same, and more particularly, to a semiconductor laser device having a narrow emission, which increases coupling loss at a junction interface between an active layer region and a waveguide layer structure. The present invention relates to a semiconductor integrated device in which increase in threshold current and decrease in luminous efficiency are suppressed, and a method for manufacturing the same.

[0002]

2. Description of the Related Art When assembling an optical module by connecting a semiconductor laser device as a light source and an optical fiber as an optical path, the semiconductor laser device to be used is considered to be easy to perform optical coupling with the optical fiber. A narrow emission semiconductor laser element having a small output beam diameter is preferable. Further, in terms of the cost of the optical module itself and the cost of the entire optical communication system incorporating the same, it is preferable that the narrow emission semiconductor laser device can be manufactured at low cost.

Here, the manufacture of a conventionally known narrow emission semiconductor laser device will be described with reference to the drawings.
First, n-InP is formed on an n-InP substrate 1 by an epitaxial crystal growth method such as MOCVD or MBE.
Lower cladding layer 2 made of nP, GaInAsP / Ga
A quantum well structure made of InAsP, an active layer 3 having a light confinement layer, and an upper cladding layer 4 made of p-InP are sequentially formed to form a slab-shaped first semiconductor layer structure I as an active layer region. (FIG. 7).

[0004] In this case, it is assumed that each of the above-mentioned semiconductor materials constituting the layer structure I is epitaxially grown such that the crystal orientation [011] is in the direction shown by the arrow in FIG. Then, a plurality of masks 5 are formed on the cladding layer 4 in the layer structure I using, for example, SiO ₂ or SiN _x.
Is patterned. FIG. 8 is a plan view showing a state near one mask.

In this case, the pattern of the mask 5 in a plan view is generally rectangular, and the shape of the edge 5a is generally orthogonal to the crystal orientation [011]. After patterning the mask 5, wet etching using, for example, a phosphoric acid-based etch cent is performed, and as shown in FIG. 9, the layer structure I located immediately below the mask 5 is left and the other parts are the substrate 1. Then, an etching surface Ia from the edge 5a of the mask 5 to the substrate 1 is formed. In that case, I in the layer structure I
Since the etching selectivity differs between nP and GaInAsP, a step occurs on the formed etching surface Ia.

Next, for example, M
GaInAsP and InP are successively selectively grown by the OCVD method. As shown in FIG. 10 and FIG. 11 which is a cross-sectional view taken along the line XI-XI in FIG. Second semiconductor layer structure functioning as waveguide layer region II
Is formed, and a butt joint joining surface J is formed between the etching surface Ia of the layer structure I and the layer structure II. Therefore, the butt joint joining surface J has a shape having a step perpendicular to the crystal orientation [011] in a plane.

The laser light oscillated in the active layer 3 of the layer structure I (active layer region) is guided to the waveguide layer 6 optically coupled to the layer structure I at the butt joint junction J, as shown in FIG.
The light is emitted as indicated by the arrow. In addition, this layer structure
Since II is formed by selective growth, its thickness increases on the layer structure I side where the mask 5 is formed, that is, on the light incident end side, and gradually decreases as the distance from the layer structure increases. It becomes thinnest at a distant point, that is, at the light emitting end. In this case, although it depends on the length of the waveguide layer 6 in the light guiding direction in the layer structure II, for example, if the length of the waveguide layer 6 is about 150 μm, the film thickness on the incident end side and the emission end Is usually 1: 1/3.
About 1/2.

After the mask 5 is removed, an etching process is performed from the upper surface of the layer structure I and the layer structure II joined to the butt joint, so that the two layer structure portions have a ridge having a predetermined width and a predetermined height. The ridge is formed into a shape, and a normal embedding operation is performed on both sides and the surface of the ridge. Finally, an intended narrow emission semiconductor laser device is manufactured through an electrode forming process.

[0009]

At the time of the selective growth of the layer structure II in the above-mentioned manufacturing process, as shown in FIG.
May crawl up and grow. In particular, when the thickness of the layer structure II is increased, the above-mentioned crawling growth becomes remarkable, and the butt joint joining surface J
Is formed at the center.

When such a situation occurs, in the element manufactured through the embedding step and the electrode forming step following the selective growth step of the layer structure II, for example, the convex portion 8 formed based on the crawling growth causes The element is J / D
When connecting with an optical fiber by passive alignment, smooth alignment of the optical axis becomes difficult, and as a result, the manufacturing cost of the optical module is increased.

Therefore, in the manufacture of the narrow emission semiconductor laser device, with respect to the layer structure II formed by selective growth, it is necessary to prevent the above-mentioned protrusion 8 from being formed on the upper surface of the butt joint joining surface J based on the creeping growth. Is required. Also, in the case of this element, since the etching surface (junction surface) Ia of the layer structure I formed at the time of the above-mentioned wet etching process has a step, abnormal growth occurs at the time of forming the layer structure II, and for example, A cavity or the like may be formed.

On the other hand, in the case of this laser device, the larger the optical coupling efficiency at the butt joint junction J between the active layer region I (layer structure I) and the waveguide layer region II (layer structure II), the better. Specifically, the optical coupling efficiency is 100
% Is best. The optical coupling efficiency is limited by the thickness of the layer structure II formed by selective growth.

Therefore, it is assumed that the thickness of the lower cladding layer 2 in the layer structure I is 2 μm, the thickness of the active layer 3 is 300 nm, and the thickness of the upper cladding layer 4 is 2 μm.
When the relationship between the thickness of the waveguide layer 6 and the optical coupling efficiency in II is calculated, the relationship is as shown in FIG. In the figure,
The solid line indicates the optical center in the thickness direction of the active layer 3 and the waveguide layer 6.
Of the optical center in the thickness direction of the optical fiber (Δd: unit is n
m) is 0, that is, when both optical centers match, and the broken line is when the above-mentioned Δd value is 100 nm.

In the latter case, when the layer structure I is etched, the end point of the etching is not the substrate surface, but
This is the case that occurs when etching is performed deeper than that. As is clear from FIG. 13, when the optical center of the active layer 3 and the optical center of the waveguide layer 6 coincide (Δd = 0), when the thickness of the waveguide layer 6 is set to about 300 nm, the butt joint bonding surface J Is 100%.

That is, 100% optical coupling efficiency can be realized at the butt joint junction surface J only after selective growth is performed until the thickness of the waveguide layer 6 in the layer structure II becomes about 300 nm. Assuming that the latter Δd =
When the layer structure I is excessively etched as in the case of 100 nm as in the case of 100 nm, it is necessary to perform selective growth so that the waveguide layer 6 in the layer structure II becomes thicker.

However, when the thick layer structure II is formed by selective growth, there is a disadvantage that the protrusion 8 is formed by creeping up and growing near the joint surface of the butt joint as described above. Such a problem, that is, the problem of the occurrence of the protrusions can be solved by reducing the film thickness of the waveguide layer 6 in the layer structure II to such an extent that crawling during selective growth does not occur. As is apparent from FIG. 13, the optical coupling efficiency is reduced, and the threshold current is increased, so that the characteristics of the laser device are deteriorated in the first place.

Furthermore, as described above, the layer structure II formed by selective growth is thicker on the layer structure I side (light incident end side) and thinner on the light emitting end side, so that the butt joint joining surface If the film thickness at J is reduced, the film thickness on the emission end face side becomes about 1/3 to 1/2 of that, and it is conceivable that the function as a waveguide is lost. For this reason, it is necessary to secure a certain thickness on the exit end side. In this case, the butt joint joining surface J
In this case, since a very thick film state is formed, crawling growth during selective growth is likely to occur.

As described above, in a semiconductor integrated device having a butt joint junction surface typified by the above-mentioned narrow emission semiconductor laser device, when a thick layer structure II is formed by selective growth, the butt joint is formed by creeping up and growing. There is a problem that a projection is formed on the upper surface of the bonding surface. Also,
When wet etching is performed on the layer structure I, there is also a problem that cavities are formed at the joint surface of the butt joint as described above.

The present invention solves the above-mentioned problem in a semiconductor integrated device in which the layer structure II is formed by selective growth, and is capable of forming a layer structure II on a mask even if the film thickness of the layer structure II at the butt joint junction surface is increased to about 300 nm. It is an object of the present invention to provide a semiconductor integrated device useful as a narrow emission semiconductor laser device that operates with a low threshold current and a high luminous efficiency without generating a convex portion based on the growth of the semiconductor device, and a method of manufacturing the same.

[0020]

According to the present invention, a first semiconductor layer structure and a second semiconductor layer structure are provided.
A semiconductor integrated structure formed on the semiconductor substrate by butt joint bonding with the semiconductor layer structure, wherein the butt joint bonding surface is formed by dry etching on the first semiconductor layer structure; 1
A semiconductor integrated element characterized by being a vertical plane inclined with respect to the crystal orientation of the semiconductor material constituting the semiconductor layer structure, preferably, the inclination angle of the butt joint joining surface is 45 ° ± 10 °. Is provided.

More specifically, an active layer region having a layer structure including an active layer and a waveguide layer region to be butt-joined therewith are formed on a semiconductor substrate, and the butt-joint surface is A semiconductor laser device is provided, which is a vertical plane inclined at least with respect to a crystal orientation of a semiconductor material constituting an active layer in a region.

Further, in the present invention, a step of forming a first semiconductor layer structure on a semiconductor substrate by an epitaxial crystal growth method; forming a mask on a surface of the first semiconductor layer structure, and then performing a dry etching process. Go, the first
Dry-etching a part of the semiconductor layer structure of the above; and forming a second semiconductor layer structure by a selective growth method on the part of the dry-etched part, thereby forming the first semiconductor layer structure and the second semiconductor layer structure. Butt-joining the semiconductor device to form a mask, wherein the edge of the mask on the side of the butt-joint surface to be formed is oriented with respect to the crystal orientation of the semiconductor material constituting the first semiconductor layer structure. A method of manufacturing a semiconductor integrated device, characterized in that the semiconductor integrated device has an inclined shape in plan view.

The semiconductor has a plan view shape comprising a central mask portion located at the center, and both side mask portions located on both sides of the central mask portion and longer than the central mask portion. A method for manufacturing an integrated device is provided. And the inclination angle of the edge of the mask is 45 °
A method for manufacturing a semiconductor integrated device, which is preferably ± 10 °, is provided.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a semiconductor integrated device according to the present invention will be described below with reference to the drawings.
11 to 11 as examples. First, as in the case shown in FIG. 7, a first semiconductor layer structure I which is an active layer region is formed on the (001) plane of a substrate 1 made of n-InP. Therefore, the crystal orientation [011] of each semiconductor material constituting the layer structure I is shown in FIG.
In the direction of the arrow (waveguide direction of laser light).

Next, a plurality of masks are formed on the upper cladding layer 4 constituting the uppermost layer of the layer structure I by using SiO ₂ or SiN _x , and then an etching process is performed. The part is etched away to the surface of the substrate 1. The greatest feature of the present invention is that the mask has the following planar shape. This will be described below.

FIG. 1 is a plan view showing a state in the vicinity of one of the plurality of masks 5 formed on the upper cladding layer 4 of the layer structure I. As is clear from FIG. 1, the mask 5 formed in the present invention is formed of a semiconductor material that forms the layer structure I by forming an edge 5a at a position where a butt joint joint surface is to be formed between the layer structure I and a layer structure II described later. It has a plan view shape that is inclined at an angle θ with respect to the crystal orientation [011].

Here, in order to realize 100% optical coupling efficiency with the layer structure I during the selective growth described later, the thickness of the layer structure II at the joint surface of the butt joint is set to about 300 nm. In order to prevent the mask 5 from crawling and growing even when the thickness is as large as
Preferably, it is set to 0 °. After such a mask 5 is formed, dry etching by RIE using, for example, CH ₄ / H ₂ is performed. A target is set so that the etching end point at that time is on the surface of the substrate 1.

The mask 5 is formed by the dry etching process.
The portion other than the portion of the layer structure I located immediately below is removed by etching, and as shown in FIG. 2, a vertical dry etching inclined at an angle θ with respect to the crystal orientation [011] is formed on the substrate 1. The layer structure I having the surface Ia remains. This dry-etched surface 1a does not have a step as in the case of an etched surface formed by wet etching. Then, this dry etching surface Ia becomes a butt joint bonding surface with a layer structure II described later.

Next, a semiconductor material for the waveguide layer and a semiconductor material for the protective layer are sequentially grown on the substrate 1 so that the second semiconductor layer structure II is formed on the etching surface Ia of the layer structure I. After joining the butt joint in the light waveguide direction, an etching process is performed from the entire upper surface to form a ridge shape having a predetermined width and height on the substrate 1. Therefore, after this step, FIG. 3 and FIG.
As shown in FIG. 4 which is a cross-sectional view taken along the line IV, the layer structure has a ridge shape, is composed of a waveguide layer 6 and a protective layer 7, and the light incident end side has an equal width ridge shape. A layer structure II butt-joined to I is formed on the substrate 1.

In the case of the butt joint joining surface J, the shape in plan view is an angle θ, specifically 45, with respect to the crystal orientation [011] of the semiconductor material forming the layer structure I.
It becomes a vertical plane inclined by ± 10 ° (FIG. 3). Although the reason is not clear, since the edge 5a of the mask 5 is inclined at an angle θ with respect to the crystal orientation [011], the waveguide layer region (layer structure II) is Even when the film thickness is about 300 nm, it does not crawl on the mask 5 and grow, and no convex portion as shown in FIG.

Next, another example will be described. This mask 9
Has a plan view shape including a central mask portion 9a located at the center and a pair of both side mask portions 9c, 9c located on both sides of the central mask portion 9b, as shown in FIG. Further, both side mask portions 9c, 9c are longer in the light guiding direction than the central mask portion 9b. Then, both side mask portions 9c, 9c and central mask portion 9b
Of the semiconductor material constituting the layer structure I has an angle θ (45 ° ± 10 °).
The inclination at (°) is the same as the case of the mask 5 shown in FIG.

When dry etching is performed on the layer structure I on which the mask 9 is formed, as shown in FIG.
A layer structure I having a dry etching surface Ia having the same shape as the mask 9 in plan view and inclined at an angle θ (45 ° ± 10 °) with respect to the crystal orientation [011] is left on the mask. Therefore, in this layer structure I, the etching surface of the central mask portion 9b and the two side mask portions 9c,
A space portion 10 having a rhombic shape in a plan view is formed between the space portion 10 and the side etching surface 9c.

When the selective growth is performed, the semiconductor material flows from the central mask portion 9b into the space portion 10 as shown by the arrow and grows as a crystal, and the semiconductor material also flows from the both side mask portions 9c, 9c. The crystal flows into the layer 10 as indicated by the arrow, and the crystal grows, thereby forming the waveguide layer region. In addition, as a matter of course, the selective growth proceeds in a portion other than the space portion 10 and a waveguide layer region is formed.

The waveguide region (layer structure I)
After the formation of I), an active layer region having a width of the central mask portion 9b is formed by performing an etching process.
A ridge shape composed of a butt joint bonded waveguide layer region is formed. Therefore, this mask 9
In the case of the laser device using the laser beam, the etched surface of the layer structure I located immediately below the central mask portion 9b functions as a butt joint bonding surface.

When the mask 9 is used, the film forming speed of the waveguide layer region in the space portion 10 is higher than the film forming speed of the other portions. If the required film thickness is required,
That is, a film thickness of, for example, about 300 nm required near the etching surface of the layer structure I immediately below the central mask portion 9b in the space portion 10 can be quickly realized.

Here, the following narrow emission semiconductor laser device was manufactured. (001) of the substrate 1 made of n-InP
On the surface, a lower cladding layer 2 made of n-InP and having a thickness of 50 nm, a strained quantum well structure of GaInAsP / GaInAsP and a thickness of 10 formed of a GaInAsP optical confinement layer.
An active layer 3 having a thickness of 0 nm and an upper cladding layer 4 having a thickness of 50 nm made of p-InP are sequentially formed by MOCVD to form a layer structure I having a crystal orientation [011] shown in FIG. The length of the central mask portion 9b is 800 μm,
Has a width of 10 μm in a direction perpendicular to the longitudinal direction, has a length of 900 μm on both side mask portions 9 c, 9 c, and has an inclination angle θ of 45 mm with respect to the crystal orientation [011].
After the mask 9 was formed, the layer structure I was dry-etched by RIE using CH ₄ / H ₂ to form the layer structure I shown in FIG.

Next, selective growth of GaInAsP and In
P was selectively grown to form a waveguide layer region having a waveguide layer and a protective layer having a thickness of 50 nm and a total length of 150 μm. In this waveguide layer region, the thickness on the emission end side is about 100 nm, and the thickness on the incidence end side is about 300 nm. Next, the mask 9 is removed to form a ridge,
Further, a laser device was formed through an embedding process and an electrode forming process.

The threshold current of this device was 2 mA.
A narrow emission laser beam having a horizontal direction of 9 ° and a vertical direction of 10 ° was obtained.

[0039]

As is clear from the above description, when the semiconductor integrated device of the present invention is used as a narrow emission semiconductor laser device, the semiconductor integrated device has a distance of 100 from the active layer region (layer structure I).
The waveguide layer region (layer structure II) can be formed by selective growth up to a film thickness of about 300 nm capable of realizing an optical coupling efficiency of about 300 nm without forming a convex portion above the boundary.

Therefore, the threshold current can be reduced and the connection with the optical fiber can be performed smoothly. Although the above description has been made with reference to the narrow emission semiconductor laser device as an example, in the device structure of the present invention, the active layer region (layer structure I) is a DFB laser device structure, and the waveguide layer structure (layer structure II). ) Can be an EA-DFB laser device by adopting the structure of an electroabsorption modulator.

[Brief description of the drawings]

FIG. 1 is a plan view showing a state in which a mask used in the present invention is formed on a layer structure I.

FIG. 2 is a perspective view showing a state after an etching process is performed on a layer structure I.

FIG. 3 is a plan view showing a butt joint joining of a layer structure I and a layer structure II.

FIG. 4 is a sectional view taken along line IV-IV in FIG. 3;

FIG. 5 is a plan view showing a state in which another mask used in the present invention is formed in a layer structure I.

6 is a perspective view showing a state after an etching process is performed on the layer structure I of FIG. 5;

FIG. 7 is a sectional view showing a layer structure I.

FIG. 8 is a plan view showing a state in which a conventional mask is formed on a layer structure I.

FIG. 9 is a cross-sectional view showing a state after performing an etching process on the layer structure I of FIG. 8;

FIG. 10 is a plan view showing a conventional butt joint joining surface formed by a layer structure I and a layer structure II.

FIG. 11 is a sectional view taken along the line XI-XI in FIG. 10;

FIG. 12 is a cross-sectional view showing the growth of the layer structure II on the mask.

FIG. 13 is a graph showing a calculation result regarding the influence of the thickness of the waveguide layer on the optical coupling efficiency.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Lower cladding layer 3 Active layer 4 Upper cladding layer 5 Mask 5a Edge of mask 5 6 Waveguide layer 7 Protective layer 8 Convex part 9 Mask 9a Edge of mask 9b Central mask part 9c Side mask part 10 Spatial part I First semiconductor layer structure (active layer region) Ia Etched surface of first semiconductor layer structure II Second semiconductor layer structure (waveguide layer region) J Butt joint interface

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Akihiko Kasukawa 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. F-term (reference) 2H047 KA03 KA13 MA05 NA04 PA24 QA02 TA32 5F073 AA64 AB21 AB25 AB28 CA12 DA25 EA19

Claims (8)

[Claims] 1. A semiconductor integrated device in which a first semiconductor layer structure and a second semiconductor layer structure are butt-joined and formed on a semiconductor substrate, wherein the butt-joint surface is the first semiconductor layer structure. A semiconductor integrated device having a vertical surface inclined with respect to a crystal orientation of a semiconductor material constituting a semiconductor layer structure. 2. The semiconductor integrated device according to claim 1, wherein said inclination angle of said butt joint joining surface is 45 ° ± 10 °. 3. An active layer region having a layer structure including an active layer and a waveguide layer region that is butt-joined to the active layer region are formed on a semiconductor substrate, and the butt-joint surface is formed at least in the active layer region. A semiconductor laser device having a vertical plane inclined with respect to a crystal orientation of a semiconductor material forming an active layer. 4. The semiconductor laser device according to claim 3, wherein said inclination angle of said butt joint joining surface is 45 ° ± 10 °. 5. A step of forming a first semiconductor layer structure on a semiconductor substrate by an epitaxial crystal growth method; forming a mask on a surface of the first semiconductor layer structure; Etching a part of the semiconductor layer structure; and forming a second semiconductor layer structure on the etched part by a selective growth method.
Bonding the semiconductor layer structure and the second semiconductor layer structure to each other with a butt joint. In the method for manufacturing a semiconductor integrated device, an edge of the mask on the side of the butt joint bonding surface to be formed is the first semiconductor layer. A method for manufacturing a semiconductor integrated device, wherein the semiconductor integrated device has a shape in a plan view inclined with respect to the crystal orientation of a semiconductor material constituting a structure. 6. The method according to claim 5, wherein the etching process is a dry etching process. 7. A plan view shape comprising a central mask portion located at the center and both side mask portions located on both sides of the central mask portion and longer than the central mask portion. Item 6. The method for manufacturing a semiconductor integrated device according to Item 5. 8. An inclination angle of an edge of the mask is 45 ° ± 1.
7. The method for manufacturing a semiconductor integrated device according to claim 5, wherein the angle is 0 [deg.].